pub(crate) fn modl_dipole_kernel(grid: &Grid, bdir: (f64, f64, f64)) -> Vec<f64>Expand description
MoDL-QSM dipole kernel D = 1/3 − (k·B̂)²/|k|² with k from fftfreq (DC at the
array corner, D[0,0,0]=0). Bit-identical to test_tools.dipole_kernel.